Exhaust gas emitted from an internal combustion engine, for example, a diesel engine, is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (CO), unburned hydrocarbons (HC) and oxides of nitrogen (NOx) as well as condensed phase materials (liquids and solids) that constitute particulate matter. Particulate filters are provided to filter the materials from the exhaust. When a particulate filter becomes full of particulates, the particulate filter is regenerated. If temperatures are too high during the regeneration process, the particulate filter may crack or melt. Thus, it is desirable to evaluate the efficiency of the particulate filter from time to time, to determine if the particulate filter is damaged.